Diffie-Hellman key exchange between OpenSSL 3, LibreSSL 3 and a custom C++ implementation. The project is just for fun. Also, you can use the project as an example of OpenSSL/LibreSSL DH/ECDH key exchange. The project can be compiled with either OpenSSL 3 or LibreSSL 3 support. A custom implementation is not available for Elliptic-curve Diffie–Hellman yet!

See below for the main classes.

• DiffieHellman is an interface for the DH key exchange implementations. Also, it provides the factory method to create an appropriate instance.
• DiffieHellmanOpenSSL is a typical OpenSSL DH key exchange implementation.
• DiffieHellmanLibreSSLDH is a typical LibreSSL DH key exchange implementation.
• DiffieHellmanLibreSSLBN is an intermediate DH key exchange implementation which is based on LibreSSL BIGNUM without using the DH functions.
• DiffieHellmanBoost is a C++ DH key exchange implementation which uses boost::multiprecision::cpp_int for big number operations.
• ECDiffieHellman is an interface for ECDH key exchange implementations. Also, it provides the factory method to create an appropriate instance.
• ECDiffieHellmanOpenSSL is a typical OpenSSL ECDH key exchange implementation.
• ECDiffieHellmanLibreSSL is a typical LibreSSL ECDH key exchange implementation.
• DHTester is a DH key exchange tester class.
• ECDHTester is a ECDH key exchange tester class.

The project uses std::format, using enum and other modern C++ features so you need latest compilers for it. See the links below.

• https://en.cppreference.com/w/cpp/compiler_support
• https://docs.microsoft.com/en-us/cpp/overview/visual-cpp-language-conformance
• https://clang.llvm.org/cxx_status.html

You also need CMake, OpenSSL (or LibreSSL) and Boost C++ (headers only). By default, LibreSSL will be used. Use cmake .. -DUSE_OPENSSL=ON If you want to compile the project with OpenSSL support.

VS 2019 v16.10 & v16.11 or later is required. Personally, I use VS 2022. The download link is here https://visualstudio.microsoft.com/vs/community/.

CMake is available as a part of VS 2022 installation. In my case it is located in the following folder: C:/Program Files/Microsoft Visual Studio/2022/Community/Common7/IDE/CommonExtensions/Microsoft/CMake/CMake/bin/. Install CMake separately https://cmake.org/ if your VS does not include it.

Download OpenSSL 3.x.x from https://www.openssl.org, unpack it.
Download the Strawberry Perl portable edition from https://strawberryperl.com and unpack it to a folder next to unpacked OpenSSL.

Open x64 Native Tools Command Prompt for VS 2022
Use any of the following commands depending on how you want to compile diffie-hellman-cpp eventually: “..\strawberry\perl\bin\perl” Configure no-asm debug-VC-WIN64A Debug, x64, /MD
“..\strawberry\perl\bin\perl” Configure no-asm VC-WIN64A Release, x64, /MD
“..\strawberry\perl\bin\perl” Configure no-asm debug-VC-WIN64A no-shared -DMT Release, x64, /MT
“..\strawberry\perl\bin\perl” Configure no-asm VC-WIN64A no-shared -DMT Release, x64, /MT

When it completes, run the following command: nmake The OpenSSL header folder can be taken from the include subfolder. The compiled libraries can be taken from the root of your OpenSSL compilation folder.

See NOTES-WINDOWS.md if the instruction above does not work.

If you want to test the project with LibreSSL support instead of OpenSSL, download the latest sources from https://www.libressl.org/ and do the): Go to the root of the unpacked LibreSSL and execute the following commands:

mkdir build
cd build
cmake .. -DCMAKE_INSTALL_PREFIX=your_libressl_installation_folder
cmake --build . --config Debug
cmake --install . --config Debug

(you can choose either Debug or Release).

See README.windows if the instruction above does not work.

Download and unpack the latest Boost C++ if you do not have it on your machine. You can compile the library if you like but it is not necessary.

Download the project, go to the root and run the following commands:

mkdir build
cd build
:: For LibreSSL
cmake .. -DINCLUDE_DIRS="your_boost_root_folder;your_libressl_installation_folder\include" -DLIBRARY_DIRS="your_libressl_installation_folder\lib"
:: For OpenSSL
cmake .. -DUSE_OPENSSL=ON -DINCLUDE_DIRS="your_boost_root_folder;your_libressl_installation_folder\include" -DLIBRARY_DIRS="your_libressl_installation_folder\lib"
:: Start compilation
cmake --build . --config Debug

(again, choose either Debug or Release according to the library builds).

If CMake is not installed, run the following command: sudo apt install cmake.

If not installed, run sudo apt install openssl openssl-dev

Download the latest LibreSSL https://www.libressl.org/ if you want to test it instead of OpenSSL. Go to the root of the unpacked LibreSSL and execute the following commands:

cmake .. -DCMAKE_INSTALL_PREFIX=your_libressl_installation_dir_prefix
cmake --build .
cmake --install .

See README.md if the instruction above does not work.

If you do not have Boost C++ installed on your machine, you have the following options:

• Install the whole Boost C++ : sudo apt install libboost-all-dev
• Install boost::multiprecision only (the package name may be different): sudo apt install libboost-mpi1.71-dev
• Download and unpack Boost C++ to access its headers.

You have to install Clang 14 to compile the project (see https://apt.llvm.org/ for updates if the instruction below does not work).

• Add the following lines to your /etc/apt/sources.list: deb http://apt.llvm.org/focal/ llvm-toolchain-focal main
  deb-src http://apt.llvm.org/focal/ llvm-toolchain-focal main
• Add signatures for these repos (otherwise apt-get update will complain in the next step): wget -O - https://apt.llvm.org/llvm-snapshot.gpg.key|sudo apt-key add -
• Run sudo apt update to add these repos to the apt.
• Install Clang 14. sudo apt install clang-14 sudo apt install libc++-14-dev libc++abi-14-dev
• Make sure now Clang 14 is used by CMake. export CXX=clang++-14

Download the project, go to the root and run the following commands:

mkdir build
cd build
# To compile with OpenSSL support; no parameters if installed to the system 
cmake .. -DUSE_OPENSSL=ON
# To compile with LibreSSL
cmake .. -DINCLUDE_DIRS="your_boost_root_folder;your_libressl_installation_dir_prefix\include" -DLIBRARY_DIRS="your_libressl_installation_dir_prefix\lib"
# Start compilation
cmake --build .

You might not need to specify the Boost C++, OpenSSL/LibreSSL folders if the libraries are installed into your system standard location.

Run the program to start the tests. You can explicitly specify the prime length in bits and the generator. See examples below:

• diffie-hellman-cpp dh DH key exchange. The prime length is 512; the generator is 2.
• diffie-hellman-cpp dh 512 5 DH key exchange. The prime length is 512; the generator is 5.
• diffie-hellman-cpp dh 256 DH key exchange. The prime length is 256 (too small for OpenSSL!); the generator is 2.
• diffie-hellman-cpp ecdh ECDH key exchange. The curve name is secp384r1.
• diffie-hellman-cpp ecdh sect571r1 ECDH key exchange. The curve name is sect571r1.